2,747 research outputs found
Proton tracking in a high-granularity Digital Tracking Calorimeter for proton CT purposes
Radiation therapy with protons as of today utilizes information from x-ray CT
in order to estimate the proton stopping power of the traversed tissue in a
patient. The conversion from x-ray attenuation to proton stopping power in
tissue introduces range uncertainties of the order of 2-3% of the range,
uncertainties that are contributing to an increase of the necessary planning
margins added to the target volume in a patient. Imaging methods and
modalities, such as Dual Energy CT and proton CT, have come into consideration
in the pursuit of obtaining an as good as possible estimate of the proton
stopping power. In this study, a Digital Tracking Calorimeter is benchmarked
for proof-of-concept for proton CT purposes. The Digital Tracking Calorimeteris
applied for reconstruction of the tracks and energies of individual high energy
protons. The presented prototype forms the basis for a proton CT system using a
single technology for tracking and calorimetry. This advantage simplifies the
setup and reduces the cost of a proton CT system assembly, and it is a unique
feature of the Digital Tracking Calorimeter. Data from the AGORFIRM beamline at
KVI-CART in Groningen in the Netherlands and Monte Carlo simulation results are
used to in order to develop a tracking algorithm for the estimation of the
residual ranges of a high number of concurrent proton tracks. The range of the
individual protons can at present be estimated with a resolution of 4%. The
readout system for this prototype is able to handle an effective proton
frequency of 1 MHz by using 500 concurrent proton tracks in each readout frame,
which is at the high end range of present similar prototypes. A future further
optimized prototype will enable a high-speed and more accurate determination of
the ranges of individual protons in a therapeutic beam.Comment: 21 pages, 8 figure
X-Ray spectra from protons illuminating a neutron star
We consider the interaction of a slowly rotating unmagnetized neutron star
with a hot (ion supported, ADAF) accretion flow. The virialized protons of the
ADAF penetrate into the neutron star atmosphere, heating a surface layer.
Detailed calculations are presented of the equilibrium between heating by the
protons, electron thermal conduction, bremsstrahlung and multiple Compton
scattering in this layer. Its temperature is of the order 40-70 keV. Its
optical depth increases with the incident proton energy flux, and is of the
order unity for accretion at -- of the Eddington rate. At
these rates, the X-ray spectrum produced by the layer has a hard tail extending
to 100 keV, and is similar to the observed spectra of accreting neutron stars
in their hard states. The steep gradient at the base of the heated layer gives
rise to an excess of photons at the soft end of the spectrum (compared to a
blackbody) through an `inverse photosphere effect'. The differences with
respect to previous studies of similar problems are discussed, they are due
mostly to a more accurate treatment of the proton penetration process and the
vertical structure of the heated layer.Comment: Accepted for publication in A&
Software environment for controlling and re-configuration of Xilinx Virtex FPGAs – TWEPP-07
The Time Projection Chamber is one of the detectors of the ALICE experiment, that is currently being commissioned at the Large Hadron Collider at CERN. The Detector Control System is used for control and monitoring of the system. For the TPC Front-End Electronics (FEE) the control node is a Readout Control Unit that communicates to higher layers via Ethernet, using the standard framework DIM. The Readout Control Unit is equipped with commercial SRAM based FPGAs that will experience errors due to the radiation environment they are operating in. This article will present the implemented hardware solution for error correction and will focus on the software environment for configuration and controlling of the system – TWEPP-07
Constraining the magnitude of the Chiral Magnetic Effect with Event Shape Engineering in Pb-Pb collisions at = 2.76$ TeV
In ultrarelativistic heavy-ion collisions, the event-by-event variation of
the elliptic flow reflects fluctuations in the shape of the initial state
of the system. This allows to select events with the same centrality but
different initial geometry. This selection technique, Event Shape Engineering,
has been used in the analysis of charge-dependent two- and three-particle
correlations in Pb-Pb collisions at TeV. The
two-particle correlator ,
calculated for different combinations of charges and , is
almost independent of (for a given centrality), while the three-particle
correlator
scales almost linearly both with the event and charged-particle
pseudorapidity density. The charge dependence of the three-particle correlator
is often interpreted as evidence for the Chiral Magnetic Effect (CME), a parity
violating effect of the strong interaction. However, its measured dependence on
points to a large non-CME contribution to the correlator. Comparing the
results with Monte Carlo calculations including a magnetic field due to the
spectators, the upper limit of the CME signal contribution to the
three-particle correlator in the 10-50% centrality interval is found to be
26-33% at 95% confidence level.Comment: 20 pages, 6 captioned figures, 1 tables, authors from page 15,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/382
X-Ray spectra from accretion disks illuminated by protons
The X-ray spectrum from a cool accretion disk heated by virialized protons is
computed. The cool disk is either embedded in a magnetically heated accretion
disk corona or partly extends into an ion supported torus (or ADAF). We
calculate the stationary equilibrium between proton heating, electron thermal
conduction and the radiative losses by bremsstrahlung and Compton scattering. A
heated surface layer on top of the accretion disk is produced with temperatures
between 60--90 keV above a cool layer with temperatures of 0.01 keV (AGN) and
1keV (galactic black hole candidates). The spectra produced by the surface
layer are reminiscent of hard state spectra, but a bit too steep, especially
for AGN's. Near the inner edge of the disk, where the optical depth of the disk
, we find that the cool component of the disk disappears.
Instead, the hot protons from the corona/ADAF heat the disk, on a dynamical
time-scale, to temperatures of several 100 keV, limited by pair production.
This region, here called a `warm disk', could contribute significantly to the
hard X-ray spectra and could be important for feeding material into an ADAF.Comment: Accepted by A&A. Includes new subsection on the applicability of
Spitzer's energy loss formula for the incident proton
The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events
The design, construction, and commissioning of the ALICE Time-Projection
Chamber (TPC) is described. It is the main device for pattern recognition,
tracking, and identification of charged particles in the ALICE experiment at
the CERN LHC. The TPC is cylindrical in shape with a volume close to 90 m^3 and
is operated in a 0.5 T solenoidal magnetic field parallel to its axis.
In this paper we describe in detail the design considerations for this
detector for operation in the extreme multiplicity environment of central
Pb--Pb collisions at LHC energy. The implementation of the resulting
requirements into hardware (field cage, read-out chambers, electronics),
infrastructure (gas and cooling system, laser-calibration system), and software
led to many technical innovations which are described along with a presentation
of all the major components of the detector, as currently realized. We also
report on the performance achieved after completion of the first round of
stand-alone calibration runs and demonstrate results close to those specified
in the TPC Technical Design Report.Comment: 55 pages, 82 figure
Energy dependence of exclusive photoproduction off protons in ultra-peripheral p-Pb collisions at = 5.02 TeV
The ALICE Collaboration has measured the energy dependence of exclusive
photoproduction of vector mesons off proton targets in
ultra-peripheral p-Pb collisions at a centre-of-mass energy per nucleon pair
TeV. The ee and decay channels
are used to measure the cross section as a function of the rapidity of the
in the range , corresponding to an energy in the
p centre-of-mass in the interval GeV.
The measurements, which are consistent with a power law dependence of the
exclusive photoproduction cross section, are compared to previous
results from HERA and the LHC and to several theoretical models. They are found
to be compatible with previous measurements.Comment: 25 pages, 3 captioned figures, 3 tables, authors from page 19,
published version, figures at http://alice-publications.web.cern.ch/node/455
Measurement of the production of charm jets tagged with D mesons in pp collisions at = 7 TeV
The production of charm jets in proton-proton collisions at a center-of-mass
energy of TeV was measured with the ALICE detector at the CERN
Large Hadron Collider. The measurement is based on a data sample corresponding
to a total integrated luminosity of , collected using a
minimum-bias trigger. Charm jets are identified by the presence of a D
meson among their constituents. The D mesons are reconstructed from their
hadronic decay DK. The D-meson tagged jets are
reconstructed using tracks of charged particles (track-based jets) with the
anti- algorithm in the jet transverse momentum range
and pseudorapidity
. The fraction of charged jets containing a D-meson
increases with from to . The distribution of D-meson tagged jets as a
function of the jet momentum fraction carried by the D meson in the
direction of the jet axis () is reported for two ranges
of jet transverse momenta, and
in the intervals
and , respectively. The
data are compared with results from Monte Carlo event generators (PYTHIA 6,
PYTHIA 8 and Herwig 7) and with a Next-to-Leading-Order perturbative Quantum
Chromodynamics calculation, obtained with the POWHEG method and interfaced with
PYTHIA 6 for the generation of the parton shower, fragmentation, hadronisation
and underlying event.Comment: 29 pages, 8 captioned figures, 3 tables, authors from page 24,
published version, figures at http://alice-publications.web.cern.ch/node/525
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Inclusive J/ψ production at mid-rapidity in pp collisions at √s = 5.02 TeV
Inclusive J/ψ production is studied in minimum-bias proton-proton collisions at a centre-of-mass energy of s = 5.02 TeV by ALICE at the CERN LHC. The measurement is performed at mid-rapidity (|y| < 0.9) in the dielectron decay channel down to zero transverse momentum pT, using a data sample corresponding to an integrated luminosity of Lint = 19.4 ± 0.4 nb−1. The measured pT-integrated inclusive J/ψ production cross sec- tion is dσ/dy = 5.64 ± 0.22(stat.) ± 0.33(syst.) ± 0.12(lumi.) μb. The pT-differential cross section d2σ/dpTdy is measured in the pT range 0–10 GeV/c and compared with state-of- the-art QCD calculations. The J/ψ 〈pT〉 and 〈pT2〉 are extracted and compared with results obtained at other collision energies. [Figure not available: see fulltext.]
The transition from a cool disk to an ion supported flow
We show that the inner regions of a cool accretion disk in an X-ray binary
can transform into an advective, ion supported accretion flow (an optically
thin ADAF, here called ISAF), through events involving only the known
properties of the Coulomb interaction in a two-temperature plasma, standard
radiation processes, and viscous heating. The optically thin inner edge of the
disk is heated to a few 100 keV by the strong flux of hot ions from the
surrounding hot ISAF. We show that he resident ions in this `warm' disk are
thermally unstable due to internal viscous heating, and heat up to their virial
temperature. The innermost disk regions thus evaporate and feed the ISAF. These
processes are demonstrated with time dependent calculations of a
two-temperature plasma in vertical hydrostatic equilibrium, including heating
by external ions, internal proton--electron energy exchange, and viscous
heating. The process complements the `coronal' evaporation mechanism which
operates at larger distances from the central object.Comment: Final version as accepted A&A. Includes new subzection on
applicability of Spitzer's energy loss formula for the incident proton
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